obj\Debug\netstandard2.0\OSPSuite.BDDHelper.AssemblyInfo.cs(16,59): warning CS7035: The specified version string does not conform to the recommended format - major.minor.build.revision [C:\projects\ospsuite-bddhelper\src\OSPSuite.BDDHelper\OSPSuite.BDDHelper.csproj]
obj\Debug\netstandard2.0\OSPSuite.BDDHelper.AssemblyInfo.cs(19,55): error CS7034: The specified version string does not conform to the required format - major[.minor[.build[.revision]]] [C:\projects\ospsuite-bddhelper\src\OSPSuite.BDDHelper\OSPSuite.BDDHelper.csproj]

It seems that the assembly patching is causing the issue, creating a version that is not valid (if I remove the assembly patching, the build is successful. However we would like to have the build performed also on PR obviously)

Is there a way to disable assembly patching on Pull request? I tried to use conditional builds using for: or on: but it did not do anything
I am sure there is a simple way to make it work but I could not find it. I would appreciate any feedback you might have

There are plans to support specializing build configuration for PR builds with a for.pull_request construct, but as of yet it's not available.

There are a few options, in order of increasing "hackey-ness"...

First, you could simply remove

pull_requests:
do_not_increment_build_number: true

from your config file, since this is appending the random string to each build, thus preventing legal patching.

Or you could keep that in and use something like assembly_version: "$(app_version).$(APPVEYOR_BUILD_NUMBER)" in the patching section, though this will result in duplicated packages.
Similarly, something like this

Thanks for getting back to me.
We'd like to avoid creating incrementing the build number everytime a PR is made if possible. This is a great feature from appveyor and it would be fantastic to be able to use it onwards.

Following on your suggestions: The only duplicate package I would get would be the one with build number 1 correct? Provided that appveyor does not have issue with multiple packages with the same version (I think it was not working a few years ago) then I should be fine.